If GM Apples Don't Brown, How Can You Tell If They're Rotten?

Soon after being sliced, a conventional Granny Smith apple (left) starts to brown, while a newly developed GM Granny Smith stays fresher looking.

Courtesy of Okanagan Specialty Fruits Inc.

Originally published on September 27, 2012 3:13 pm

In the fairy-tale world, a shiny red apple can lead to a poisonous end. But some see two genetically engineered green apple varieties, poised to become the first to gain U.S. Department of Agriculture approval,as similar harbingers of doom.

Okaganan Specialty Fruits Inc., the company that has developed Granny Smith and Golden Delicious varieties that don't go brown when you slice them, says the fears are overblown and the apples are safe to eat.

Now, we've reported extensively on the heated debate over labeling genetically engineered food, and there's no denying that genetically modified (GM) foods are a polarizing issue. But would an apple that doesn't turn brown prevent us from telling whether it's rotten? The short answer is no. For the long answer, read on.

The non-browning trait aims to please consumers who don't like brown apples or the off taste from the preservatives frequently used to maintain color and fresh appearance in packages of pre-sliced apples, says Neal Carter, Okanagan's president. "Ultimately, we just want people to eat more apples," he says. Carter also argues the innovation would help apple slice producers, who can lose up to half of their product from browning during production.

Nevertheless, as the public comment period on a petition to approve these apples closed last month, many consumers worry — are they safe to eat?

First, let's look at the physical properties of apples. No matter how you slice it, every apple turns brown eventually. "When their flesh is cut, the oxygen in the air interacts with chemicals in the flesh of the apple," says Susan Brown, a plant scientist at Cornell University. An enzyme called polyphenol oxidase, or PPO, makes melanin, an iron-containing compound that gives apple cells a brown tinge. The same type of "oxidative" browning happens in the browning of tea, coffee or mushrooms, explains Brown.

Within five minutes of slicing, browning can alter the taste and might not be as aesthetically pleasing, but it doesn't mean the apple is old or rotten.

To prevent oxidative browning, the GM apples developed by Okanagan stop PPO production with a man-made gene containing pieces of four natural PPO genes. An insertion with gene fragments is an automatic red flag for the apple cell — usually the first step of viral attack — so it chops up every sequence of DNA that looks like the suspicious fragment, and the apple flesh stays light.

"The beauty of this [process] is it's a natural plant defense mechanism," says Carter. Even when sliced, these apples stay clear of browning for about two weeks — that's roughly the same extended life span as apple slices from McDonald's and Burger King, which use lemon juice and calcium ascorbate to prevent browning.

But if the apple doesn't go brown, then how do you tell if it's rotten? An apple with just oxidative browning isn't automatically rotten. Rotting comes from a fungal or bacterial infection, which causes the apple to go either mushy or dry. Infecting spores, not melanin, also give the flesh a dark brown hue. So, taking PPO out of the equation won't make a rotten apple appear pristine. "'Bad' apples will still be evident," says Brown. Rotting GM apples look rotten and turn brown from a bacterial or fungal infection the same as a conventional apple.

But Bill Freese, a science policy analyst at the Center for Food Safety, notes that some studies in tomatoes have shown that silencing PPO has an impact on a plant's susceptibility to diseases and invasive insects because the enzyme may play a role in plant defense reactions.

From nutrient value to taste, these apples are indistinguishable from a normal one, say Carter and Brown. If they do gain USDA approval, whether people will buy them is another story. "It's up to the consumer to decide," Brown says.

As we've reported before, many of our processed foods that contain soy or corn are genetically modified, but fresh produce has been a tougher sell. Anybody remember the Flavr Savr tomato?

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